This disclosure relates to foamed acid technologies, and more specifically, to foamed chelating agent treatment fluids for production enhancement treatments, such as matrix stimulation, in subterranean well bores and for the efficient dissolution of scale and fouling of associated equipment.
In many instances, it is desirable to stimulate hydrocarbon-producing intervals in subterranean formations to improve productivity or remove damage. Several means are available to accomplish the desired stimulation. In carbonate formations such as limestone and dolomite, hydrochloric acid and certain organic acids (e.g., formic acid and acetic acid) may be injected, often under pressure, to etch channels, dissolve formation materials in pore spaces, and improve well productivity. Another production stimulation treatment known as fracture-acidizing involves the formation of one or more fractures in the formation and the introduction of an aqueous acidizing fluid into the fractures to etch the fracture faces, whereby flow channels are formed when the fractures close. The aqueous acidizing fluid also enlarges the pore spaces in the fracture faces and in the formation, thereby increasing the permeability of the formation. “Acidizing” as used herein refers to both fracture acidizing and matrix acidizing.
In carrying out acidizing treatments in certain subterranean zones, the acidizing fluid used can be lightweight to prevent excessive hydrostatic pressure from being exerted on the subterranean zone, e.g., when such zone is prone to fracturing. As a result, a variety of lightweight acidizing fluids have heretofore been developed and used, including foamed acidizing fluids. In addition to being lightweight, a foamed acidizing fluid contains compressed gas which improves the ability of the acidizing fluid to backflow out of a subterranean zone that has been acidized and undergo subsequent recovery. Another benefit is the diverting effect that foamed acidizing fluids have over nonfoamed acidizing fluids.
Foamed acidizing fluids have heretofore involved the use of hydrochloric acid. Hydrochloric acid is a strong acid that presents safety concerns at the wellsite and presents corrosion and toxicity limitations. Additionally, such acidizing fluids may not meet complete environmental regulations when, due to temperatures in excess of 200° F., specific additives like corrosion inhibitors have to be used in regulated areas. In other instances, the use of hydrochloric acid may be precluded by the metallurgical composition of the specific alloys making up the infrastructure of an operation. For instance, some transport pipelines are not made of the same steel alloy that is used in subterranean installations dedicated to extracting underground energetic resources. Other metallurgical alloys are also present in various industrial operations, like those dedicated to the transport of steam from geothermal extractive processes. Such alloys include, for instance, copper-alloys. These alloys cannot be judiciously exposed to hydrochloric acid-containing fluids.
Additionally, it may be desirable to improve the productivity of or remove damage from equipment that is often associated with subterranean well bores. Such equipment includes, for example, piping, heat exchangers, and associated turbines. Examples of such piping includes existing pipeline installations, such as those that carry produced hydrocarbon-containing fluids from a well site to a refinery, or energetic fluids like steam produced from a geothermal reservoir to an electricity generating station. Completion installations such as inflow control valves for instance are other examples. Removing the scale from the interior of a pipeline may be very difficult. Scaling deposits, which may include copper, silica, barium, iron and calcium scales, for example, can reduce the functionality of such equipment and decrease the flow rate through the equipment. In heat exchangers specifically, such scale deposits may lead to unbalanced, less efficient heat exchange.